1. Field of the Invention
The present invention generally relates to a disk apparatus and its disk medium and a method of formatting the disk medium, and more particularly, to a disk apparatus and a method of formatting a disk medium which moves a recording-and-reproducing head on the disk medium by using a rotating-type actuator.
2. Description of the Related Art
Recently, as an external storage unit for a computer, etc., a magnetic disk apparatus is widely used. For increasing a storage capacity of the storage unit, it is desired to improve the packing density of a disk medium as a recording medium. For this purpose, a magnetoresistance-effect head (MR head) using a magnetoresistive element (MR element) is also in use. Also, in use of such a MR head, it is desired to realize a high packing density of the disk medium. For this purpose, a track pitch in the disk medium needs to be decreased as much as possible.
FIG. 1 shows a top plan view of an example of the conventional magnetic disk apparatus. In a magnetic disk apparatus 11 shown in FIG. 1, an actuator 12 comprises an arm 13, a supporting spring 13a connected to the arm 13, and a magnetic head 14 mounted at a top end of the supporting spring 13a. A basic part of the arm 13 is supported by a pivot 15, which allows the arm 13 to be freely rotated.
On an opposite side of the pivot 15 of the arm 13, a rotation supporting part 16 is formed, and a coil 17 is wrapped around the rotation supporting part 16. Under the coil 17, two magnets 18a, 18b are fixed. The coil 17 and the magnets 18a, 18b construct a voice coil motor (VCM).
The arm 13 of the actuator 12 is rotated by a current flow to the coil 17 from a wiring board 21 through a flexible print board 22. This allows movement of the magnetic head 14 in a radial direction of a magnetic disk 20. The disk is supported by a spindle 19 of a sensorless-type spindle motor. The disk is rotated by the spindle 19.
For the magnetic head 14, though the MR head having the MR element is used for high packing density, the MR head can be used only for reproducing. Therefore, in practical use, a composite-thin-film magnetic head, in which the MR head and a recording head (in general, thin-film head) are combined, is used for the magnetic head 14.
FIGS. 2A, 2B show a configuration of the conventional composite-thin-film magnetic head. FIG. 2A shows a perspective view of the head, and FIG. 2B shows a cross-sectional view thereof. In the composite-thin-film magnetic head, a magnetoresistance-effect head (MR head) 31 comprises a rectangular magnetoresistive element (MR element) 33 formed on a non-magnetic substrate 32, pull-out conductive layers 34a, 34b (will be described later), and upper and lower magnetic sealed layers 35a, 35b.
The pull-out conductive layer 34 is cut at a given width in the lengthwise direction of the MR element 33, and is connected to both sides of an MR of the MR element 33. The MR element 33 and the pull-out conductive layer 34 are arranged between the upper magnetic sealed layer 35a and the lower magnetic seal layer 35b and is electrically insulated by non-magnetic insulating layers 36.
On the other hand, a electro/magneto-converter-type recording head (inductive head) 37 of the composite-thin-film magnetic head 14 records information to the magnetic disk 20. In the recording head 37, the upper magnetic sealed layer 35a of the MR head 31 is used as a lower magnetic transducer, and on it, a recording gap 38 including alumina (Al.sub.2 O.sub.3), an interlayer insulating layer 39 made of thermosetting resin, a thin-film coil conductive layer (Cu) 40, and an upper magnetic transducer (NiFe) 41 are layered in that order. By the recording gap 38 formed with the upper magnetic transducer and the lower magnetic transducer (the upper magnetic sealed layer) 35a, a horizontal recording of the information is carried out. Further, a protecting insulating layer 42 is formed on the upper magnetic transducer 41.
In this way, the composite-thin-film magnetic head 14 is formed by composing the MR head 31 and the recording head 37 in the lengthwise direction of the track in the magnetic disk 20. Therefore, the recording gap 38 of the recording head 37 and the MR element 33 are located with a gap of an interval L from each other.
In the meantime, when the magnetic head 14 is moved in the radial direction of the magnetic disk 20 by a swinging movement of the actuator 12, a crossing angle (YAW angle) between the track and the above gap L changes in the radial direction of the magnetic disk 20. In a case where the magnetic head is not the composite-thin-film magnetic head but a single inductive head, it is known that in the area of a large YAW angle (outer area or inner area), the packing density can be improved by the track pitch being close (Japanese Laid-Open Patent Application No.55-18060). In the case of the composite-thin-film magnetic head, since there is the interval L between the recording gap 38 and the MR head 33, even if the large YAW angle is obtained in the outer area or the inner area, it is difficult to densify the track pitch.
FIGS. 3A and 3B show illustrations for explaining a conventional method of setting the track pitch. FIG. 4 shows an illustration for explaining a position relationship between the magnetic head and the track in FIGS. 3A, 3B. In FIGS. 3A and 3B, the recording gap 38 of the recording head 37 is represented by a track width of a write core, and the MR element 33 of the MR head 31 is represented by a track width of a read core. The interval between the write core and the read core is L.
As shown in FIG. 3A and FIG. 4, in the composite-type magnetic head 14, if core widths of the write core 37 (38) and the read core 33 are the same and the YAW angle is set to .+-.10 degree, the core width of the read core 33 is wider than a core width of the track, and extends over a portion of an adjoining track. Therefore, undesired noise from the adjoining track makes the S/N ratio decrease.
To adjust the read core 33 within the core width (a+b+c=d) when the YAW angle is a maximum value .+-.10 degree, the width of the read core 33 is usually set to a width c (shaded part) based on when the YAW angle is 0 degree.
As shown in FIG. 3B, in the magnetic disk 20, dead spaces DSs are set in both sides of the track so as to prevent signals on adjoining tracks A, C from being erased due to magnetic-head position fluctuating by servo performance degradation, offtrack, and vibration, etc., when writing data on track B.
FIG. 3B shows a case where one side of the write core 37 (38) and one side of the read core 33 are aligned when the YAW angle is maximum (.+-.10 degree). In this case, the dead space DS is set to be equal to or greater than a maximum positioning error according to a positioning accuracy so as not to erase data in the track C when the head is shifted to the track C during writing the data on the track B. An interval between center lines of the two dead space DSs is given the term track pitch TP.
In FIG. 3B, the track pitch TP is set by using the following equations.
The width c of the read core is represented as follows: EQU c=d-L.multidot.{tan(maximum YAW angle)-tan(minimum YAW angle)}!.(1)
The second term L.multidot.{tan(maximum YAW angle)-tan(minimum YAW angle)}! of the equation (1) represents a maximum loss with the YAW angle. An actual loss e with the YAW angle is represented as follows: EQU e=L.multidot.tan(.vertline.YAW angle.vertline.). (2)
Therefore, the track pitch TP is represented as follows: EQU TP=c+e+DS. (3)
In the above equation (3), (c+e) is the width d of the write core.
For example, in the case of a magnetic disk of 3.5 inches, the width d of the write core 37 (38) is set to 6 .mu.m, the width c of the read core 33 is set to 4 .mu.m, and the dead space DS is set to 1 to 2 .mu.m. Therefore, the track pitch is 7 to 8 .mu.m, and as a result, the packing density of the magnetic disk 20 is determined.
A narrower track pitch increases the packing density of the magnetic disk 20. The narrower track pitch enables the amount of information per a unit area to increase. However, since the dead space DS is required for the positioning accuracy, it is difficult to decrease the dead space DS. Therefore, the width d of the write core 37 (38) needs to be decreased. However, there is a problem that the width c of the read core 33 is also decreased with the decrease of the width d. Thus, decreased width c makes a read-out signal level decrease.
Another method to compensate the degradation due to the width c of the read core 33 decreasing is by improving head performance, magnetic disk characteristics, and demodulator performance. However, this method makes the magnetic disk apparatus expensive, increases size, and is complex. Thus, there is a problem of increasing the packing density.